1. Field of the Invention
The present invention relates to an apparatus for X-ray CT photography.
2. Description of the Background Art
Conventionally, X-ray CT photography is performed in a medical field and the like. In the X-ray CT photography, a subject is irradiated with an X-ray to collect projection data, and the obtained projection data is reconstructed on a computer to generate a CT (Computed (Computerized) Tomography) image.
In the X-ray CT photography, the subject is disposed between an X-ray generator and an X-ray detector, the X-ray generator and the X-ray detector turn about the subject, and the X-ray generator emits conical X-ray (an X-ray cone beam) to subject. The X-ray detector collects an X-ray detection result (the projection data), and three-dimensional data (volume data) is reconstructed based on the collected X-ray detection result. For example, Japanese Patent Application Laid-Open No. 2010-42121, PCT Application International Publication No. WO 2007/046372, and Japanese Patent Application Laid-Open No. 11-19078 (1999) disclose apparatuses that perform the X-ray CT photography.
Japanese Patent Application Laid-Open No. 2010-42121 discloses an X-ray CT photographic apparatus configured to perform both the X-ray CT photography and panoramic photography. In this apparatus, a detection signal is read from a whole X-ray detection surface of a planar X-ray receiver in the X-ray CT photography, and the X-ray detection signal is read in a limited way only from the point irradiated with an X-ray beam in the X-ray detection surface of a planar X-ray receiver in the panoramic photography.
PCT Application International Publication No. WO 2007/046372 discloses a medical digital X-ray photographic apparatus configured to be able to perform plural kinds of X-ray photography modes, and a read region of the X-ray detection signal of an X-ray sensor is changed in each mode.
In the X-ray CT photographic apparatus disclosed in Japanese Patent Application Laid-Open No. 11-19078 (1999), during the X-ray CT photography, a pair of channel collimators is displaced in front of an X-ray generator, and only an interest region of a subject (a patient) is irradiated with an X-ray such that a shape of CT photographic region (FOV (Field of View)) becomes a circle or an ellipse.
In the X-ray CT photographic apparatus disclosed in Japanese Patent Application Laid-Open No. 2010-42121, the X-ray detection signal is read from the whole surface of the X-ray detector during the X-ray CT photography. In performing local X-ray CT photography in which the X-ray CT photography is restricted to a local portion of the subject, although only part of the detection surface of the X-ray detector is irradiated with the X-ray, the X-ray detection signal is read from a portion that is not irradiated with the X-ray. Therefore, there is a risk of degrading transfer efficiency of the X-ray detection signal.
In the medical digital X-ray photographic apparatus disclosed in PCT Application International Publication No. WO 2007/046372, the read region of the X-ray detection signal is fixed during the X-ray CT photography. The useless X-ray detection signal is read in the case that the portion irradiated with the X-ray changes every moment in the detection surface of the X-ray detector during the X-ray CT photography. Accordingly, there is a risk of degrading the transfer efficiency of the X-ray detection signal.
In the X-ray CT photographic apparatus disclosed in Japanese Patent Application Laid-Open No. 11-19078 (1999), the portion irradiated with the X-ray changes in the detection surface of the X-ray detector by regulating an X-ray irradiation range. However, in this Japanese Patent Application Laid-Open No. 11-19078 (1999), there is no description about the read of the X-ray detection signal from the X-ray detector. Therefore, in the case that the X-ray detection signal is read from the whole detection surface, the read of the useless X-ray detection signal is generated to generate the risk of degrading the transfer efficiency of the X-ray detection signal.